(a) Field of the Invention
The present invention relates to an apparatus and method for inspecting a phase angle error of a camshaft for an internal combustion engine.
(b) Description of the Related Art
Generally, a camshaft is driven at one-half crankshaft speed in a four-stroke-cycle engine by either a gear, a chain and sprocket, or a cog belt and sprocket. The camshaft has as many cams as the number of intake and exhaust valves. The cams are formed at a predetermined phase angle to open and close the valves at a controlled rate of speed, as well as at precise times in relation to piston position.
Therefore, if the phase angle becomes mis-aligned when manufacturing the camshaft, precise valve timing cannot be attained, lowering the performance of the engine. It is therefore necessary to check the phase angle error of each camshaft. The following method is typically used to inspect the phase angle error.
The phase angle of a camshaft is measured by an apparatus and then compared with a design phase angle to determine if the camshaft is fit for use in an actual engine. A well known apparatus for measuring the phase angle is the three-dimensional measuring apparatus.
The three-dimensional measuring apparatus comprises a detector moving along X, Y and Z axes perpendicular to each other, and a measuring device that reads the amount of movement of the detector along the axes and measures a position and outer shape of an object. The phase angle of a camshaft can be measured using such a three-dimensional measuring apparatus.
However, the three-dimensional measuring apparatus is expensive. One reason for the high cost is that the three-dimensional measuring apparatus is designed to make various measurements (i.e., location, distance, outline, and shape) of numerous different objects in addition to the phase angle of camshafts. Also, the measuring process is complicated, increasing the amount of time needed to measure the camshaft phase angle, as well as requiring a skilled operator to perform the measurements.